1. Field of the Invention
This invention relates to apparatus including a magnetic variation pick-up means, disposed against a rotor having a tooth to be detected, for outputting a pulse signal which cyclically rises and falls as the tooth comes close to and leaves away from the pick-up means according to a signal from the pick-up means, and detecting the rotational position of the rotor according to the rising and the falling edges of the pulse signal.
2. Description of the Related Art
As shown in FIG. 26, there has been a known a rotating speed detecting apparatus (JP-A-3-220414) for detecting the number of automotive engine revolutions, including a magnet 120 for magnetic field biasing, disposed against magnetic-material teeth 110a of a rotor 110 rotating in synchronism with engine rotation, and a molded IC package enclosing a Hall element containing a magnetic variation detecting circuit 150 between the rotor 110 and the magnet 120. In FIG. 26, reference numeral 130 denotes a case made of a non-magnetic material, 141 denotes an input/output pin, 140 denotes a molded IC package and 142 denotes a wiring board.
The magnetic variation detecting circuit 150, from output of the Hall element, obtains a cyclic signal Di which becomes strongest when a tooth 110a of the rotor 110 is on the pick-up center line CL and becomes weakest when a groove 110b between the adjacent teeth is on the pick-up center line as shown in FIG. 27. This prior-art magnetic variation detecting circuit 150 successively detects points in time (indicated by upward arrows) where the cyclic signal Di has varied by a predetermined amount of hysteresis HYS from when the cyclic signal Di starts to increase, and outputs a low level signal "0", and also successively detects points in time (indicated by downward arrows) where the cyclic signal Di has varied by a predetermined amount of hysteresis HYS from when the cyclic signal Di starts to decrease, and outputs a high level signal "1". In other words, the magnetic variation detecting circuit outputs a rotational speed signal SO in a pulse form which is at the low level when a tooth 110a is located against the pick-up position and which is at the high level when a groove 110b is located against the pick-up position. This rotational position signal SO is input to a computer for automotive engine control and is used to calculate the rotating speed of the rotor 110, or the like.
The apparatus constructed as described can be applied to a cylinder discriminating sensor in the automotive engine, for example. In such an application, as shown in FIG. 28, a rotor 210 is used which has only a large projected tooth 210a with a central angle of 180.degree. and a large groove 210b with a central angle of 180.degree..
However, in this prior-art magnetic variation detector circuit, the starting pulse form of the rotational position signal SO is determined once the cyclic signal Di has started to increase or decrease. Therefore, immediately after the engine is started, the rotational position signal SO has not yet been determined. What is referred to as immediately after the engine start is when the crankshaft is beginning to rotate by a starter, and also immediately after a power supply to a sensor is turned on. For this reason, immediately after the engine is started (immediately after the power is turned on), though the tooth 110a or 210a is located on the pick-up center line CL at the engine start (hereafter referred to as "start from a projected portion"), a high level signal is sometimes output as an initial value, and even though the groove 110b or 210b is located on the pick-up center line CL at the engine start (hereafter referred to as "start from a recessed portion"), a low level signal is sometimes output as an initial value. As a result, the conventional apparatus is sometimes unable to detect timing of the initial transition from a tooth to a groove or from a groove to a tooth just after the engine start.
In other words, at a start from a projected portion, as shown in FIG. 29A, though it is ideal to start with a low level signal, if the initial value of the SO signal is at the high level, the SO signal starts from the high level and continues to be at the high level until the tooth comes around. On the other hand, at a start from a recessed portion, as shown in FIG. 29B, though it is ideal to start from a high level, the SO signal sometimes starts from a low level and continues to be at the low level. In those cases, it is impossible to detect an initial timing of passage of an edge portion from a tooth 110a to a groove 110b or from a groove 110b to a tooth 110a.
Therefore, particularly in the cylinder discriminating sensor of a gasoline engine, the ignition timing in the first combustion stroke sometimes cannot be calculated, leaving high chances for the fuel/air mixture drawn into the cylinder not to be ignited and burnt, and exhausted into the atmospheric air.